From: Eric Hodel <drbrain@...7.net>
Date: 2011-11-03T07:00:48+09:00
Subject: Re: Ruby and Telnet

On Nov 2, 2011, at 2:57 AM, Leo M. wrote:
> Because I want to perform a smtp reverse lookup!

What is "smtp reverse lookup"?

Do you mean DNS reverse lookup?  You can do that with this script:

require 'resolv'

Resolv::DNS.open do |dns|
  res = dns.getresources ARGV.shift, Resolv::DNS::Resource::IN::MX
  exchanges = {}
  res.each do |r|
    exchanges[r.exchange] = r.preference
  end

  forward = Hash.new { |h, k| h[k] = [] }

  exchanges.each_key do |exchange|
    res = dns.getresources exchange, Resolv::DNS::Resource::IN::A

    res.each do |r|
      forward[exchange] << r.address
    end
  end

  forward.each do |exchange, addresses|
    addresses.each do |address|
      res = dns.getresources address.to_name, Resolv::DNS::Resource::IN::PTR

      res.each do |r|
        puts "MX #{exchange} #{exchanges[exchange]}"
        puts "\thas address #{address}"
        puts "\twith reverse #{r.name}"
      end
    end
  end
end